All-organic-based photovoltaic solar cells have attracted considerable attention because of their lowcost
processing and short energy payback time. In such systems the primary dissociation of an optical
excitation into a pair of photocarriers has been recently shown to be extremely rapid and efficient,
but the physical reason for this remains unclear. Here, two-dimensional photocurrent excitation
spectroscopy, a novel non-linear optical spectroscopy, is used to probe the ultrafast coherent decay
of photoexcitations into charge-producing states in a polymer:fullerene based solar cell. The twodimensional
photocurrent spectra are interpreted by introducing a theoretical model for the description
of the coupling of the electronic states of the system to an external environment and to the applied
laser fields. The experimental data show no cross-peaks in the twodimensional photocurrent spectra, as
predicted by the model for coherence times between the exciton and the photocurrent producing states
of 20fs or less.